Because ATF gets to decide, on a case by case basis, what is and isn't an MG. They can also change their mind at any time and declare a previously approved item is now an MG and force the maker to recall/buyback all his product. All subject to the whims of whoever is in charge at any given time, the individual examiner that catches the job that day, etc.

350 bucks poorer when you have to turn it in. When they told Akins his toy was being reclassified, he had to recall them. IIRC, they finally accepted that as long as the spring was gone, it was OK as it didn't work without it.

Atkins had a spring that made it work automatically by just depressing the trigger. The SSAR 15 requires intentional forward pushing of the forearm of the weapon to make it work. Also Atkins never actually sent the ATF a working model of the model they sold. They instead sent a model for the SKS which broke immediately during testing and never actually worked. However, it seems the ATF did say that they did approve the actual concept of the Atkins. Slide fire solutions sent the actual model they are selling, so I think it may be a little harder, but not impossible for the ATF to rescind the approval.